Efficiency of Driveshafts have not been analyzed in great detail in the past due to their relatively high efficiency. However, it is possible to obtain about a 0.1 percent increase in fuel economy by decreasing driveshaft torque losses by about 20 percent, owing to the combination mode fuel calculation. In order to improve fuel economy it is necessary to increase the efficiency of the constant velocity universal joint (C.V.J.) used for driveshafts. Additionally, propeller shafts with improved heat characteristics are required. It is for these reasons that this project is conducted.In this paper, the motion of two typical joint used for front-engine, front-drive passenger cars is analyzed geometrically and efficiency formulas are derived. One of the joints is a Rzeppa joint, used on the wheel side of the driveshaft and the other is a tripot joint, used on the differential side. These formulas are then verified by experiment.It is found that about 70 percent of frictional induced losses in a Rzeppa joint are due to internal friction caused by contact of the inner and outer spherical surface with the cage. Similarly 70 percent of frictional induced losses in a tripot joint are caused by internal friction which is a result of contact between the balls and the grooves of the housing. Therefore, the motivation to improve fuel economy and heat characteristics can be seen.